The present invention relates to a method and device for recording data on rewritable or write-once optical discs, which permit optimal recording with minimized possibility of reproduction failure and reproduction errors.
Phase-change optical discs are known today as an example of rewritable optical discs and generally classified into Type 1 and Type 2 discs in terms of their behaviors and recording speeds. The so-called "overwrite recording" on the Type 1 phase-change optical disc uses a single laser light beam which is varied among three different energy or power intensity values Pw, Pe and Pb, as shown at (a) in FIG. 2. The first value Pw represents intensity of "writing power" for transforming the recording layer of the disc from its original crystallized state to an amorphous state so as to form pits in the layer. The second value Pe represents intensity of "erasing power" for restoring the amorphous state of the recording layer to the original crystallized state so as to erase (overwrite) the formed pits. The third value Pb represents intensity for "bottom power (base power)" that correspond to bottom power of pulses in the so-called "divided-pulse recording" and acts to prevent heat diffusion resulting from the laser light beam irradiation during the recording. The pulse-dividing period is typically set to the length of 1 T in the conventional CD format, although it may be set to any other suitable time length. With such a laser light beam varied among the three power intensity values Pw, Pe and Pb, each pit is formed continuously over a length corresponding to a predetermined number of divided pulses, as shown at (b) in FIG. 2.
For the overwrite-recording on the Type 2 phase-change optical disc or recording on the write-once optical disc, a single laser light beam is used which is switched between two respective intensity values of the writing power Pw and the erasing power Pe (or bottom power Pb), as shown in FIG. 3.
The optimum writing power intensity value Pwo of the laser light beam differs among various types of optical disc, and hence the writing power intensity value Pwo is typically determined by tentatively writing or test recording input signals prior to actual recording of the signals. According to the CD-Write Once (CD-WO) standards, an area to be used for the test recording, commonly known as a PCA (Power Calibration Area), is reserved along the innermost edge of each optical disc, and the optimum writing power intensity value Pwo is set through a series of operations commonly known as "OPC" (Optimum Power Control).
In the conventionally-known OPC operations, the test recording is carried out by varying the writing power intensity value Pw step by step as shown in FIG. 4, and the test-recorded area is then reproduced, and an asymmetry value (index indicating asymmetry of HF signals) .beta. is calculated, for each of the varied intensity values Pw, as a characteristic parameter representing the recording quality of the signals as shown in FIG. 5. Then, the writing power intensity value Pw resulting in an optimal asymmetry value (e.g., 0.04) is set as the optimum writing power intensity value Pwo to be used in the actual recording. Conventionally, the erasing power Pe and bottom bottom power Pb are set to fixed intensity values that were predetermined through experiments.
However, the conventionally-known techniques had the problem that the erasing power and bottom power of fixed intensity values would often result in reproduction failure or errors due to non-uniform and time-varying conditions of various discs used, different specifications of the disc makers, etc.